Percutaneous access devices and bone anchor assemblies

ABSTRACT

A percutaneous access device includes an inner tube and an outer tube disposed about at least a portion of the inner tube. The outer tube may be sized to span from a skin incision in a patient to a site proximate the spine of the patient. The distal end of the outer tube may be adapted to releasably engage a bone anchor. The inner tube may be adjustable relative to the outer tube between a first position and a second position in which the distal end of the inner tube contacts the bone anchor. A bone anchor assembly includes a bone anchor having a distal bone engaging portion and a receiving member having a recess for receiving a spinal fixation element. The proximal end of the receiving member may have an arcuate groove formed on an exterior surface thereof to facilitate connection of an instrument to the receiving member.

BACKGROUND

For a number of known reasons, spinal fixation devices are used inorthopedic surgery to align and/or fix a desired relationship betweenadjacent vertebral bodies. Such devices typically include a spinalfixation element, such as a relatively rigid fixation rod or plate, thatis coupled to adjacent vertebrae by attaching the element to variousanchoring devices, such as hooks, bolts, wires, or screws. The fixationelements can have a predetermined contour that has been designedaccording to the properties of the target implantation site, and onceinstalled, the fixation element holds the vertebrae in a desired spatialrelationship, either until desired healing or spinal fusion has takenplace, or for some longer period of time.

Spinal fixation elements can be anchored to specific portions of thevertebrae. Since each vertebra varies in shape and size, a variety ofanchoring devices have been developed to facilitate engagement of aparticular portion of the bone. Pedicle screw assemblies, for example,have a shape and size that is configured to engage pedicle bone. Suchscrews typically include a threaded shank that is adapted to be threadedinto a vertebra, and a head portion having a rod-receiving element,usually in the form of a U-shaped recess formed in the head. Aset-screw, plug, or similar type of closure mechanism is used to lockthe fixation element, e.g., a spinal rod, into the rod-receiving head ofthe pedicle screw. In use, the shank portion of each screw is threadedinto a vertebra, and once properly positioned, a rod is seated throughthe rod-receiving member of each screw and the rod is locked in place bytightening a cap or other closure mechanism to securely interconnecteach screw and the fixation rod.

Recently, the trend in spinal surgery has been moving toward providingminimally invasive devices and methods for implanting bone anchors andspinal fixation devices.

SUMMARY

Disclosed herein are percutaneous access devices that facilitate thedelivery and implanting of bone anchors into bone, in particular, one ormore vertebral bodies of the spine. In particular, the disclosedpercutaneous access devices permit the delivery and implanting of one ormore bone anchors in a minimally invasive manner thereby limiting traumato surrounding tissue. Moreover, the percutaneous access devicesdisclosed herein can provide a percutaneous pathway between a skinincision and the bone anchor that may be used to deliver components ofthe bone anchor, such as the fastening mechanism, the fixation element,and/or instruments to the bone anchor. Also, disclosed herein are boneanchors that facilitate the connection of instruments, such as apercutaneous access device, to the bone anchor.

In accordance with one exemplary embodiment, a percutaneous accessdevice includes an inner tube and an outer tube disposed about at leasta portion of the inner tube. The outer tube, in the exemplaryembodiment, is sized to span from at least a skin incision in a patientto a predetermined site proximate the spine of the patient. The distalend of the outer tube may be adapted to releasably engage a bone anchor.The inner tube, in the exemplary embodiment, may be adjustable relativeto the outer tube along the longitudinal axis of the outer tube betweena first position and a second position in which the distal end of theinner tube contacts the bone anchor.

In accordance with another exemplary embodiment, a bone anchor assemblyincludes a bone anchor having a proximal head and a distal bone engagingportion and a receiving member coupled to the bone anchor. The receivingmember, in the exemplary embodiment, may have a proximal end, a distalend and a recess for receiving a spinal fixation element, such as a rodor a plate. The proximal end of the receiving member, in the exemplaryembodiment, may have at least one arcuate groove formed on an exteriorsurface thereof to facilitate connection of an instrument, such as apercutaneous access device, to the receiving member.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the percutaneous accessdevices and bone anchor assemblies disclosed herein will be more fullyunderstood by reference to the following detailed description inconjunction with the attached drawings in which like reference numeralsrefer to like elements through the different views. The drawingsillustrate principles of the percutaneous access devices and bone anchorassemblies disclosed herein and, although not to scale, show relativedimensions.

FIG. 1 is a perspective view of an exemplary embodiment of apercutaneous access device;

FIG. 2 is a perspective view of the components of the percutaneousaccess device of FIG. 1;

FIG. 3 is a perspective view of the distal end of the percutaneousaccess device of FIG. 1;

FIG. 4 is a perspective view of the distal end of the percutaneousaccess device of FIG. 1 coupled to an exemplary embodiment of a boneanchor assembly;

FIG. 5 is a side elevational view of the bone anchor assembly of FIG. 4;

FIG. 6 is a side elevational view of the receiving member of the boneanchor assembly of FIG. 4;

FIG. 7 is a side elevational view in cross-section of the distal end ofthe percutaneous access device of FIG. 1 coupled to the receiving memberof the bone anchor assembly of FIG. 4;

FIG. 8 is a side elevational view in cross-section of the distal end ofthe outer tube of the percutaneous access device of FIG. 1 and thereceiving member of the bone anchor assembly of FIG. 4;

FIGS. 9 and 10 are side elevational views in cross section of the distalend of the inner tube of the percutaneous access device of FIG. 1 andthe receiving member of the bone anchor assembly of FIG. 4;

FIGS. 11A-11D are perspective views of the distal end of thepercutaneous access device of FIG. 1 and the receiving member of thebone anchor assembly of FIG. 4, illustrating exemplary steps forreleasably coupling the distal end of the percutaneous access device tothe receiving member of the bone anchor assembly;

FIG. 12 is a side elevational view an another exemplary embodiment of abone anchor assembly;

FIG. 13 is a side elevational view of the receiving member of the boneanchor assembly of FIG. 12;

FIG. 14 is a side elevational view in cross section of the receivingmember of the bone anchor assembly of FIG. 12;

FIG. 15 is a side elevational view in cross section of an arcuate grooveof the receiving member of the bone anchor assembly of FIG. 12;

FIG. 16 is a side elevational view in cross-section of the distal end ofthe another exemplary embodiment of a percutaneous access device coupledto the receiving member of the bone anchor assembly of FIG. 12;

FIGS. 17A and 17B are perspective views of an alternative embodiment ofa percutaneous access device and a bone anchor assembly, illustrating athreaded connecting between the percutaneous access device and the boneanchor assembly;

FIGS. 18A and 18B are perspective views of an alternative embodiment ofa percutaneous access device and a bone anchor assembly, illustrating aplurality of externally threaded removable tabs for releasableengagement with an instrument such as a percutaneous access device;

FIGS. 19A-19D are perspective views of an alternative embodiment of apercutaneous access device and a bone anchor assembly, illustrating thepercutaneous access device and the bone anchor assembly interconnectedby one or more internal wires;

FIGS. 20A-20D are perspective views of an alternative embodiment of apercutaneous access device and a bone anchor assembly, illustrating thepercutaneous access device and the bone anchor assembly interconnectedby one or more external wires;

FIG. 21 is a perspective view of an alternative embodiment of a boneanchor assembly having a plurality of removable tabs for releasableengagement with an instrument such as a percutaneous access device;

FIGS. 22A-22B are perspective views of an exemplary embodiment of apercutaneous access device, illustrating axial cut-outs provided in theouter tube of the percutaneous access device; and

FIGS. 23A-23B are perspective views of an alternative embodiment of apercutaneous access device and a bone anchor assembly, illustratingflexible tabs provided on the distal end of the percutaneous accessdevice for releasable engagement with the bone anchor assembly.

DETAILED DESCRIPTION

Certain exemplary embodiments will now be described to provide anoverall understanding of the principles of the structure, function,manufacture, and use of the percutaneous access devices and bone anchorassemblies disclosed herein. One or more examples of these embodimentsare illustrated in the accompanying drawings. Those of ordinary skill inthe art will understand that the percutaneous access devices and boneanchor assemblies specifically described herein and illustrated in theaccompanying drawings are non-limiting exemplary embodiments and thatthe scope of the present invention is defined solely be the claims. Thefeatures illustrated or described in connection with one exemplaryembodiment may be combined with the features of other embodiments. Suchmodifications and variations are intended to be included within thescope of the present invention.

The articles “a” and “an” are used herein to refer to one or to morethan one (i.e. to at least one) of the grammatical object of thearticle. By way of example, “an element” means one element or more thanone element.

The term “distal” as used herein with respect to any component orstructure will generally refer to a position or orientation that isproximate, relatively, to the bone surface to which a bone anchor is tobe applied. Conversely, the term “proximal” as used herein with respectto any component or structure will generally refer to a position ororientation that is distant, relatively, to the bone surface to which abone anchor is to be applied.

The terms “comprise,” “include,” and “have,” and the derivativesthereof, are used herein interchangeably as comprehensive, open-endedterms. For example, use of “comprising,” “including,” or “having” meansthat whatever element is comprised, had, or included, is not the onlyelement encompassed by the subject of the clause that contains the verb.

FIGS. 1-5 illustrate an exemplary embodiment of a percutaneous accessdevice 10. The exemplary percutaneous access device 10 can facilitatethe delivery and implanting of a bone anchor, such as the exemplary boneanchor assembly 100 illustrated and described below, into bone, inparticular, one or more vertebral bodies of the spine. In particular,the exemplary percutaneous access device 10 can facilitate the deliveryand implanting of a bone anchor in a minimally invasive manner and canprovide a percutaneous pathway between a skin incision in the patent andthe bone anchor that may be used to deliver components of the boneanchor, such as the closure mechanism, one or more fixation elements,and/or instruments to the bone anchor. The percutaneous access device 10is preferably adapted to be introduced through a minimally invasivepercutaneous incision, which is a relatively small incision thattypically has a length less than the diameter or width of the devicebeing inserted therethrough. Although the exemplary percutaneous accessdevice 10 described below is designed primarily for use in spinalapplications, one skilled in the art will appreciate that the exemplarypercutaneous access device 10, as well as the other exemplaryembodiments described below, may be used to facilitate the implantationof any type of bone anchor to any type of bone.

The exemplary percutaneous access device 10 includes an inner tube 12and an outer tube 14 disposed about at least a portion of the inner tube12. In the illustrated exemplary embodiment, the outer tube 14 iscoaxially disposed about the inner tube 12 such that the inner tube 12and the outer tube 14 share a common longitudinal axis 16. One skilledin the art will appreciate, however, that the outer tube 14 and innertube 12 need not be coaxially aligned. The inner tube 12 and the outertube 14, in the exemplary embodiment, are generally cylindrical inshape, having an approximately circular cross-section. One skilled inthe art will appreciate, however, the inner tube 12 and the outer tube14 may have other cross-sectional shapes, including, for example,elliptical or rectilinear. In the exemplary embodiment, the inner tube12 and outer tube 14 have analogous cross-sections, however, one skilledin the art will appreciate the inner tube 12 and the outer tube 14 canhave different cross-sectional shapes. The axial length of the innertube 12 and outer tube 12 may vary depending on, for example, thepatient anatomy, the procedures employed, and/or, that area of the spinein which the device 10 is employed. The inner tube 12 and the outer tube14 may be linear, as in the exemplary embodiment, or may curved orangled along one or more sections or the entire length thereof. Theinner tube 12 and the outer tube 14 may be constructed from any suitablebiocompatible material, including, for example, a metal, such asstainless steel, or a polymer, from any conventional method ofmanufacturing medical devices.

Although the illustrated exemplary embodiment includes an inner tube andan outer tube, one skilled in the art will appreciate that any number oftubes, e.g., one or more tubes, may be employed depending on, forexample, the type of bone anchor employed and the manner by which thedevice is releasably engaged to the bone anchor. For example, exemplaryembodiments of a percutaneous access device having a single outer tubeare described below.

Continuing to refer to FIGS. 1-5, the inner tube or sleeve 12 includes aproximal end 20, a distal end 22, and a lumen 24 extending between theproximal end 20 and the distal end 22. The lumen 24 extends the lengthof the inner tube 12 and defines a longitudinal axis 26 of the innertube 12. The outer tube or sleeve 14 includes a proximal end 30, adistal end 32, and a lumen 34 extending between the proximal end 30 andthe distal end 32. The lumen 34 may extend the length of the outer tube14 and defines a longitudinal axis 36 of the outer tube 14. The innertube 12 in positionable within the lumen 36 of the outer tube 14. In theexemplary percutaneous access device 10, the inner tube 12 islongitudinally adjustable with respect to the outer tube 14. Forexample, the inner tube 12 may adjustable from a first, proximalposition, in which the distal end 22 of the inner tube 12 is positionedproximal to the distal end 32 of the outer tube 14 as illustrated inFIG. 3, and a second, distal position, in which the distal end 22 of theinner tube 12 is positioned proximate to the distal end 32 of the outertube 14. In the exemplary embodiment, the distal end 22 of the innertube 12 preferably contacts at least a portion of the bone anchorassembly when the inner tube 12 is in the second position, asillustrated in FIGS. 4 and 7 and as discussed in more detail below.

The exemplary percutaneous access device 10 may include an adjustmentmechanism 40 that allows an operator to adjust the relative longitudinalposition of the inner tube 12 and the outer tube 14. In the illustratedembodiment, for example, the adjustment mechanism 40 is a hollow,tubular shaped cap 41 having internal threads 42 that engage externalthreads 44 provided on the proximal end 30 of the outer tube 14. Thethreads 42, 44 allow the cap 41 to be longitudinal adjusted relative tothe outer tube 14. In the exemplary embodiment, the inner tube 12 isconnected to the cap 41 and, thus, can move with cap 41 as the cap 41 isadvanced or withdrawn relative to the outer tube 14. For example, theproximal end 30 of the inner tube 12 of the exemplary embodiment mayinclude one or more resilient tabs 46, one or more of which may have aprojection 48 that seats within an annular grove provided on theinterior surface of the cap 41 to thereby connect the proximal end 30 ofthe inner tube 12 to the cap 41. In the illustrated embodiment, tworesilient tabs 46 are provided on opposite sides of the outer tube 14.The projection 48, in the exemplary embodiment, is sized to rotate within the groove provided in the cap 41, thus allowing the cap 41 to rotaterelative to the inner tube 12. The resilient tabs 46 are radiallyflexible to facilitate connection to and removal from the cap 41. Oneskilled in the art will appreciate that other configurations forconnecting the inner tube 12 to the cap 41 are possible and are withinthe scope of the present disclosure.

The inner tube 12 may be inhibited from rotating with respect to theouter tube 14, limiting the relative motion of the inner tube 12 and theouter tube 14 to along the longitudinal axis 16 of the percutaneousaccess device. For example, one or more resilient tabs 56 may beprovided on the inner tube 12 approximately midway between the proximalend 20 and the distal end 22 of the inner tube 12, although otherpositions are possible. In the illustrated embodiment, two resilienttabs 56 are provided on opposite sides of the outer tube 14. One or moreof the resilient tabs 56 may include a projection 58 that is sized andshaped to seat within a longitudinal slot 54 provided in the outersleeve 14. The resilient tab 56 can be radially flexible to facilitateinsertion into and removal from the slot 54. The projection 58 can slidewithin the slot 54 and, thereby can limit the relative motion betweenthe inner tube 12 and the outer tube 14 to along the longitudinal axis16 of the percutaneous access device 10. One skilled in the art willappreciate that other configurations for connecting the inner tube 12 tothe outer tube 14 are possible and are within the scope of the presentdisclosure.

The inner tube 12 may have one or more sidewall openings or slots 60formed therein. In the illustrated exemplary embodiment, the inner tube12 includes two opposed slots 60 that extend longitudinally from thedistal end 22 of the inner tube 12. Like the inner tube 12, the outertube 14 may have one or more sidewall openings or slots 62 formedtherein. In the illustrated exemplary embodiment, the outer tube 14includes two opposed slots 62 that extend longitudinally from the distalend 32 of the inner tube 12. The slots 60 and 62 can be used tofacilitate positioning of a spinal fixation device, such as a rod or aplate, relative to one or more bone anchors. Methods and devices forspinal fixation element placement are disclosed in commonly ownedco-pending U.S. patent application Ser. No. ______, filed concurrentlyherewith, entitled Method and Devices for Spinal Fixation ElementPlacement (Attorney Docket No. 101896-210) and commonly owned co-pendingU.S. patent application Ser. No. ______, filed concurrently herewith,entitled Method and Devices for Minimally Invasive Spinal FixationElement Placement (Attorney Docket No. 101896-209), both of which areincorporated herein in by reference. To facilitate positioning of aspinal fixation element, the slots 60 and the slots 62 are preferablyaligned with one another along at least a portion of the longitudinalaxis of the percutaneous access device 10. The width and length of theslot 60 and slot 62 may be varied depending on the particular methods,instruments, and fixation elements being employed. In one exemplaryembodiment, for example, the length of the slots 60 and 62 is selectedto span at least from the skin incision to the distal end of the innertube 12 and the outer tube 14, respectively. In such embodiments, theslots 60 and 62 may be accessible from outside of the patient. Inanother exemplary embodiment, the length of the slots 60 and 62 isselected to span from the distal end of the inner tube 12 and the outertube 14, respectively, to a point distal to the skin incision. In suchembodiments, the slots 60 and 62 may be accessible only from the lumensof the inner and outer tubes.

In embodiments in which multiple slots are employed, the slots 60, 62need not be similarly sized (width and/or length). For example, the oneor more slots 60 may be sized differently than the one or more slots 62,the one or more of the slots 60 on the inner tube may be sizeddifferently than other slots 60, and/or one or more of the slots 62 onthe outer tube may be sized differently than other slots 62. Althoughthe exemplary embodiment includes two opposing slots on the inner tube12 and the outer tube 14, respectively, one skilled in the art willappreciate that any number of slots may be provided, e.g., no slots,one, two, three, etc. slots, may be provided depending on the method,instruments, and/or fixation element employed.

One skilled in the art will appreciate that the slots 60 and 62 areoptional and that in certain embodiments slots may not be provided.

Referring to FIGS. 1-5 and 7, the percutaneous access device 10 ispreferably releasably engageable to a bone anchor. In the exemplaryembodiment, the outer tube 14 may be releasably engaged to a boneanchor, such as bone anchor assembly 100. For example, the outer tube 14may be engaged to a bone anchor in a manner that allows the percutaneousaccess device 10 to be connected to the bone anchor 100 during use,e.g., during implantation and/or delivery and/or fastening of a spinalfixation element to the bone anchor, and allows the percutaneous accessdevice to be disconnected from the bone anchor 100 at the conclusion ofthe procedure. Preferably, the percutaneous access device 10 can bedisconnected remotely. For example, the exemplary embodiment, thepercutaneous access device 10 can be disconnected from the bone anchorby manipulation of the proximal end of the percutaneous access device10, as discussed in more detail below.

The distal end 32 of the outer tube 14 includes a pair of opposedlongitudinally extending tabs 70A and 70B that may releaseable engage abone anchor. In the exemplary embodiment, the tabs 70A and 70B aredefined by the sidewalls of the outer tube 14 and are separated by slots62A and 62B. In certain exemplary embodiments, the tabs 70A and 70B maybe flexible and resilient in the radial direction to facilitateconnection to a bone anchor. For example, the tabs 70A and 70B may beflexed apart in the radial direction from a first, relaxed position tofacilitate advancement of the tabs longitudinally over a portion of thebone anchor. Once positioned about a portion of the bone anchor, thetabs 70A and 70B may provide a radially compressive force on the boneanchor as the tabs 70A and 70B attempt to return to the first, relaxedposition. In other exemplary embodiments, including the exemplarypercutaneous access device 10, the tabs 70A and 70B need not be flexibleand resilient.

In the illustrated exemplary embodiment, each tab 70A and 70B mayinclude one or more radially inward facing projection 72 that is sizedand shaped to seat within an opening provided in a portion of the boneanchor. The size, shape and number of projections can be varieddepending on, for example, the opening(s) provided on the bone anchorand type of connection desired. In the illustrated exemplary embodiment,for example, each projection 72A, 72B is generally arcuate in shape andhas a cross section that is complementary to an arcuate groove 130provided in the spinal fixation element receiving member 108 of theexemplary bone anchor assembly 100 described below. In particular, theprojection 72A has a distal surface 74, a proximal surface 76, and agenerally radially facing connecting surface 78 that spans between thedistal surface 74 and the proximal surface 76, as shown in FIG. 8. Inthe illustrated embodiment, the distal surface 74 is generally orientedperpendicular to the longitudinal axis of the outer tube 14 and theconnecting surface 78 is generally oriented parallel to the longitudinalaxis of the outer tube 14 and perpendicular to the distal surface 74.One or both of the proximal surface 76 and the distal surface 74 may beoriented at an angle other than perpendicular to the longitudinal axisof the outer tube 14. For example, the proximal surface 76 may beoriented at an angle A to an orthogonal line 80, which is orientedperpendicular to the longitudinal axis of the outer tube 14. In theexemplary embodiment, the angle A may be approximately 5° toapproximately 30° and is preferably approximately 20°. The distalsurface 74 and the proximal surface 76 may be oriented at the same angleor, as in the exemplary embodiment, may be oriented at different angles.

Referring to FIGS. 2, 3, 4, 7, 9 and 10, the distal end 22 of the innertube 12 may include a contact surface 81 that contacts at least aportion of a bone anchor when the inner tube 12 is in the secondposition. In the illustrated exemplary embodiment, for example, thedistal end 22 of the inner tube 12 may have two opposing generallyarcuate contact surfaces 81. The contact surfaces 81, in the exemplaryembodiment, are oriented approximately perpendicular to the longitudinalaxis of the inner tube 12. In the illustrated exemplary embodiment, thecontact surfaces 81 are configured to contact a generally arcuatecontact surface provided on the proximal end of the receiving member ofthe exemplary bone anchor assembly 100. Preferably, the contact surface81 is complementary in size, shape, and orientation to the contactsurface on the bone anchor. One skilled in the art will appreciate thatthe configuration of the contact surface 81, e.g., number, size, shape,and orientation of the contact surface 81, may be varied to, forexample, suit the bone anchor being employed.

The distal end 22 of the inner tube 12 and/or the distal end 32 of theouter tube 14 may be configured to inhibit rotation of the bone anchorassembly relative to the percutaneous access device 10. For example, thedistal end 22 of the inner tube may include one or more finger-likeextensions 82 that extend approximately axially from the distal end 22of the inner tuber 12 and engage a bone anchor to inhibit rotation ofthe bone relative to the percutaneous access device. For example, one ormore of the extensions 82 may seat within a groove, recess, slot, orsimilar structure provided in the bone anchor. Alternatively, one ofmore of the extensions 82 may include a contact surface 84 forcontacting an axially extending surface of the bone anchor, as in thecase of the exemplary embodiment and as discussed in detail below.

FIGS. 5-6 illustrate an exemplary embodiment of a bone anchor assembly100 that is particularly suited for use with the exemplary percutaneousaccess device 10 described. One skilled in the art will appreciate,however, that the percutaneous access devices disclosed herein are notlimited to use with the exemplary bone anchor assembly 100 but insteadmay be configured for use with any type of bone anchor, e.g., bone screwor hook; mono-axial or polyaxial. Exemplary bone anchor assembly 100includes a bone screw 102, such as a pedicle screw, having a proximalhead 104 and a distal bone engaging portion 106, which in theillustrated exemplary embodiment is an externally threaded screw shank.The exemplary bone screw assembly 100 also includes a receiving member108 that is configured to receive and couple a spinal fixation element,such as a spinal rod or spinal plate, to the bone anchor assembly 100.

The receiving member 108 may be coupled to the bone anchor 102 in anywell-known conventional manner. For example, the bone anchor assemblymay be poly-axial, as in the present exemplary embodiment in which thebone anchor 102 may be adjustable to multiple angles relative to thereceiving member 108, or the bone anchor assembly may be mono-axial,e.g., the bone anchor 102 is fixed relative to the receiving member 108.An exemplary poly-axial bone screw is described U.S. Pat. No. 5,672,176,incorporated herein by reference. In mono-axial embodiments, the boneanchor 102 and the receiving member may be coaxial or may be oriented atangle with respect to one another. In poly-axial embodiments, the boneanchor may biased to a particular angle or range of angles to provide afavored angle the bone anchor. Exemplary favored-angle bone screws aredescribed in U.S. Patent Application Publication No. 2003/0055426 andU.S. Patent Application Publication No. 2002/0058942, both of which areincorporated herein by reference.

The receiving member 108 of the illustrated exemplary embodimentincludes a proximal end 110, a distal end 112, and a recess or slot 114for receiving a spinal fixation element such as a spinal rod. Theproximal end 110 of the receiving member 108 has a first bore 116defining a first bore axis 118. The recess 114 communicates with thefirst bore 116 such that a spinal fixation element may be positionedthrough the first bore 116 into the recess 114. The distal end 112 has asecond bore 120 opposite the second bore 116 and defining a second boreaxis 122. The second bore axis 122 is designed to receive the head 104of the bone anchor 102 to couple the bone anchor 102 to the receivingmember 108. In the illustrated exemplary embodiment, the head 104 isseated within the second bore 116. As the exemplary illustratedembodiment of the bone anchor assembly is poly-axial, the bone anchor102 is free to rotate relative to the receiving member 108 such that thelongitudinal axis 124 of the bone anchor 102 is positionable at an anglerelative to the second bore axis 120. The second bore 116 may beconically shaped to facilitate adjustment of the bone anchor 102relative to the receiving member 108. In favored-angled embodiments, thesecond bore axis 122 may be positioned at an angle (other than 0°) tothe first bore axis 118. In the illustrated embodiment, the first boreaxis 118 and second bore axis 122 are coaxial. In the exemplaryembodiment, the receiving member 108 has a generally U-shapedcross-section defined by two legs 124A and 124B separated by recess 114.Each leg 124A, 124B is free at the proximal end 110 of the receivingmember 108.

The receiving member 108 may be configured to receive a closuremechanism that locks a spinal fixation element within the recess 114.The closure mechanism may be a cap that is advanceable through the firstbore 116 of the receiving member 108 and seats against the spinalfixation element. For example, the cap may have external threads thatengage internal threads 148 provided in the receiving member 108, e.g.,on the legs 124A,B, as in the exemplary embodiment. Any type ofconventional closure mechanism may be employed, including, for example,non-threaded caps, multi-component closure mechanisms, and/or externalcaps.

The receiving member 108 of the exemplary bone anchor assembly 100 isconfigured to be releasably connected to an instrument such as theexemplary percutaneous access device 10 described above. For example,the receiving member 108 may include at least one groove 130 that isconfigured to receive a portion of an instrument to releasably connectthe instrument to the bone anchor assembly. The size, shape, position,and number of grooves can be varied depending on, for example, theinstrument employed and the type of connection desired. In certainembodiments, for example, at least one arcuate groove 130 may beprovided on an exterior surface of the proximal end 110 of the receivingmember 108. In other exemplary embodiments, at least one arcuate groovemay be provided on an interior surface of the proximal end 110 of thereceiving member 108. In the illustrated exemplary embodiment, each leg124A and 124B may be provided with an arcuate groove 130A, 130B,respectively, at the free, proximal end of the leg 124A, 124B. Thegrooves 130A, 130B may extend about a portion or all of thecircumference of the proximal end of each leg 124A, 124B. Each groove130A, 130B may have size and shape that is complementary in size andshape to a projection provided on the instrument. For example, in theillustrated exemplary embodiment, the each groove 130A, 130B may bearcuate and may have a cross-section complementary to the cross-sectionof a projection 72A,72B provided on the tabs 70A,70B of the outer sleeve14. In particular, groove 130 may have a distal surface 132, a proximalsurface 134 and an interconnecting surface 136 that spans between thedistal surface 132 and the proximal surface 134, as illustrated in FIG.8. The distal surface 132 and/or the proximal surface 134 may beoriented to facilitate insertion of a projection into the grove 130and/or to inhibit undesirable separation of the projection from thegroove 130. In the illustrated exemplary embodiment, for example, thedistal surface 132 may be generally oriented at an angle B to anorthogonal line 140, which is oriented perpendicular to the longitudinalaxis of the receiving member 108, to facilitate insertion of theprojection into the groove. In the exemplary embodiment, the angle B maybe approximately 00 to approximately 45° and preferably approximately30° to 40°. In the illustrated exemplary embodiment, the proximalsurface 134 may be oriented at an angle other than perpendicular tolongitudinal axis of the receiving member 108 to inhibit separation ofthe projection from the groove 130, particularly in radial direction.For example, the proximal surface 134 may be oriented at an angle C toan orthogonal line 142, which is perpendicular to the longitudinal axisof the receiving member 108. In the exemplary embodiment, the angle Cmay be approximately 5° to approximately 30° and is preferablyapproximately 20°. The distal surface 132 and the proximal surface 76may be oriented at the same angle or, as in the exemplary embodiment,may be oriented at different angles. The grooves 130A and 130B, as wellas any additional grooves, may have similar cross-sectional geometries,as in the case of the illustrated exemplary embodiment, or may havedistinct geometries.

Referring to FIGS. 7 and 8, the proximal surface 76 of each projection72 may be oriented at an angle A that is approximately equal to theangle C of the proximal surface 134 of the corresponding groove. In onepreferred embodiment, for example, angle A and angle C are eachapproximately 200. One skilled in the art will appreciate that angle Aand angle C need not be approximately equal but instead, may beseparate, distinct angles.

The proximal end 110 of the receiving member 108 may include one or morecontact surfaces that may be contacted by an instrument such as thepercutaneous access device 10. In the illustrated exemplary embodiment,for example, the proximal end of each leg 124A, 124B may include one ormore generally arcuate, proximally facing contact surfaces 145.

The outer diameter of the percutaneous access device may be selected tobe approximately equal to the outer diameter of the bone anchor tofacilitate insertion of the bone anchor into the body through apercutaneous pathway of minimal size. For example, in the illustratedexemplary embodiment, the outer diameter of the outer tube 14, indicatedby line D₁ in FIG. 7, at at least the distal end 32 of the outer tube14, is approximately equal to, or less than, the outer diameter of thereceiving member 108, indicated by line d₁ in FIGS. 6 and 7. Forexample, the diameter of the outer tube 14 may taper from a proximaldiameter D₂ to a distal diameter D₁ at the distal end 32 of the outertube 14. Alternatively, the outer diameter of the outer tube 14 may beapproximately equal to, or less than, the outer diameter of thereceiving member 108 along the entire length of the outer tube 14. Toaccommodate the outer tube 14, the proximal end 110 of the receivingmember 108 may have a diameter d₂ that is less than the diameter d₁ of adistal section of the receiving member 108, as illustrated in FIG. 6.For example, the diameter d₂ proximal to the grooves 130A,B may be lessthan the diameter d₁ of the receiving member 108 to provide a reduceddiameter portion 150 at he proximal end 130 of the receiving member. Thedistance between the exterior surface of reduced diameter portion 150and the exterior surface of the receiving member 108, indicated by lineE in FIGS. 6 and 8, is preferably greater than or approximately equal tothe radial thickness of a tab 70A, 70B, as indicated by line F in FIG.8.

To facilitate delivery of devices to the bone anchor assembly throughthe percutaneous access device 10, the inner diameter of the lumen 24 ofthe inner tube 12, indicated by line F in FIG. 7, at at least the distalend of the inner tube 12, may be greater than or approximately equal tothe inner diameter of at least a portion of the receiving member,indicated by line f in FIG. 7.

Exemplary operation of the percutaneous access device 10 with theexemplary bone anchor assembly will be described with reference to FIGS.11A-11D. To releasably connect the percutaneous access device 10, thedistal end 32 of the outer tube 14 is oriented such that tabs 70A and70B are aligned with recess 114, as illustrated in FIG. 11A. Thepercutaneous access device 10 is advanced distally until each tab 70A,70B is positioned between the legs 124A and 124B, as illustrated in FIG.11B. The percutaneous access device 10 may be rotated about itslongitudinal axis 16 to rotate projections 72A, 72B into grooves 103B,130A, respectively, as illustrated in FIG. 11C. The inner tube 12 may beadvanced distally along the longitudinal axis 16 of the percutaneousaccess device 10 from the first, proximal position, illustrated in FIGS.11A-C, to the second, distal position, illustrated in FIG. 11D, in whichthe contact surfaces 81 of the inner tube 12 contact the contactsurfaces 145A, 145B provided on the proximal end of the receiving memberof the exemplary bone anchor assembly 100, to thereby releasably connectthe percutaneous access device 10 to the bone anchor assembly 100. Thecontact surface 84 of one or more of the extensions 82 may engage theaxial extending contact surfaces 152 (FIGS. 5 and 6) to inhibit rotationbetween the percutaneous access device and the bone anchor assembly.

The percutaneous access device 10 may be connected to the exemplary boneanchor assembly 100, or another bone anchor assembly, beforeimplantation of the bone anchor assembly or after the bone anchorassembly is implanted into the patient's body.

Once the percutaneous access device 10 is releasably connected to thebone anchor assembly 100 as illustrated in FIGS. 1 and 11D, thepercutaneous access device 10 may provide a percutaneous pathway betweenthe skin incision and the bone anchor 100 that facilitates delivery ofinstruments, spinal fixation elements, and/or components of the boneanchor assembly, such as the closure mechanism, to the bone anchorassembly 100. In the illustrated exemplary embodiment, for example, thelumen 24 provides a pathway to the first bore 116 of the receivingmember 108 of the bone anchor assembly 100, that may allow a closuremechanism, such as a threaded cap, to be delivered to the receivingmember 108 of the bone anchor assembly and/or may allow a screw driveror the like to be advanced into engagement with the head 104 of the boneanchor 102. Moreover, in the illustrated exemplary embodiment, the slots60 of the inner tube and the slots 62 of the outer tube 14 may bealigned with the recess 114 provided in the receiving member 108.Alignment of the slots 60 and 62 with the recess 114 facilitates thedelivery of a spinal fixation element to the bone anchor assembly.Exemplary methods and devices for delivering a spinal fixation elementto a bone anchor assembly are described in commonly owned, co-pendingU.S. patent application Ser. No. ______, filed concurrently herewith,entitled Methods and Devices for Minimally Invasive Spinal FixationElement Placement (Attorney Docket No. 101896-209) and commonly owned,co-pending U.S. patent application Ser. No. ______, filed concurrentlyherewith, entitled Methods and Devices for Spinal Fixation ElementPlacement (Attorney Docket No. 101896-210), each of which isincorporated herein in by reference.

The percutaneous access device 10 may be released from the bone anchorby rotating the percutaneous access device 10 about its longitudinalaxis 16 and retracting the device 10 distally.

FIGS. 12-16 illustrate an alternative exemplary embodiment of a boneanchor assembly 200 and an exemplary percutaneous access device 300 thatmay be configured to releasably engage the bone anchor assembly 200. Theexemplary bone anchor assembly 200 is analogous in construction to theexemplary bone anchor assembly 10 described above, except that thereceiving member 208 of the bone anchor assembly 200 has a generallyconstant outer diameter d₁, as illustrated in FIGS. 14 and 16, at theproximal end 110 thereof, and, thus, lacks the reduced diameter portion150 of bone anchor assembly 100. As a result, the outer diameter of thedistal end 32 of the outer tube 14 of the exemplary percutaneous accessdevice 300, indicated by line D₂ in FIG. 16, may be approximately equalto or, as in the illustrated embodiment, may be greater than thediameter d₁ of the proximal end 110 of the receiving member 208. Theouter diameter of the outer tube 14 may be constant, as in theillustrated exemplary embodiment, or may vary along the length of theouter tube 14.

FIGS. 17A and 17B illustrate an alternative embodiment of a percutaneousaccess device 350 and a bone anchor assembly 400, in which thepercutaneous access device and the bone anchor assembly areinterconnected by threads. For example, the percutaneous access device350 may have an outer tube 352 having a distal end 354 provided withininternal threads that releasably engage external threads 406 provided onthe proximal end 412 of the receiving member 408 of the bone anchorassembly 400. Preferably, the external threads 406 are clocked tofacilitate alignment of the grooves 62, if any, provided on the outertube 14 with the recess 414 provided in the receiving member 408. In theillustrated exemplary embodiment, the percutaneous access device 350includes a single tube, outer tube 352; an inner tube may be providedbut is not necessary.

FIGS. 18A and 18B illustrate an alternative embodiment a bone anchorassembly 500, in which the receiving member 508 includes one or moreremovable, externally threaded tabs 502 that provide a threadedconnecting between the percutaneous access device 350 and the boneanchor assembly 500. In the illustrated exemplary embodiment, a pair ofproximally extending tabs 502A and 502B extend from the legs 524A and524B, respectively. Each tab 502, in the illustrated exemplaryembodiment, is generally arcuate in shape and includes external threadsfor engagement with internal threads provided on the percutaneous accessdevice. The tabs 502 may include internal threads 415 to facilitateadvancement of a closure mechanism to the bone anchor assembly. Tabs 502may be sheared off the bone anchor assembly 500 by over tightening ofthe percutaneous access device 350 or, alternatively, may be removedfrom the bone anchor assembly 500 after withdrawal of the percutaneousaccess device 350 by a suitable instrument.

FIGS. 19A-19D illustrate an alternative embodiment of a percutaneousaccess device 550 and a bone anchor assembly 600, in which thepercutaneous access device 500 and the bone anchor assembly 600 arereleasably interconnected by one or more internal wires 551. In theillustrated exemplary embodiment, for example, a pair of wires 551,extend axially through opposing side walls of the outer tube 552. Eachwire extends through parallel axial holes provided in the side walls ofthe outer tube 552. Each wire 551 may form a loop 553 that can engagethe receiving member 608 of the bone anchor assembly. The wires may beformed of any suitable biocompatible material including, for example ametal, such as a stainless, or a polymer. The receiving member 608, inthe exemplary embodiment, includes two pairs of axially extending holes611 for receiving wires 551. Each pair of holes 611 may terminate in agroove 613 oriented perpendicular to the holes 611. The number of wiresand holes provided in the outer tube and the receiving member may bevaried depending on the application. Each wire 551 may be tensioned tocouple the percutaneous access device 550 to the bone anchor assembly.The wires 551 may be tensioned by, for example, retracting the wires 551distally. Releasing the tension on the wires 551 by, for example,cutting the wires 551 or advancing the wires 551 proximally, can releasethe percutaneous access device 550 from the bone anchor assembly 600. Inthe illustrated exemplary embodiment, the percutaneous access device 550includes a single tube, outer tube 552; an inner tube may be providedbut is not necessary.

FIGS. 20A-20D illustrates an alternative embodiment of a percutaneousaccess device 650 and a bone anchor assembly 700 in which thepercutaneous access device 650 and the bone anchor assembly 700 arereleasably interconnected by one or more externally positioned wires551. The illustrated exemplary embodiment, wires 551 extend axiallyalong the exterior surface of the outer tube 652 of the percutaneousaccess device 650 and extend axially along the exterior surface of thereceiving member 708 of the bone anchor assembly 700. The outer tube 652may include one or more axially oriented grooves 653 in which the wires551 may be seated. Likewise, the receiving member 708 may include one ormore grooves 707 in which the wires 651 may be seated. The number ofwires and/or grooves may be varied depending upon the particularapplication. In the illustrated embodiment, for example, a pair ofparallel grooves 653 are provided in opposing sidewalls of the outertube 652 and a pair of parallel of grooves 707 are provided in theopposing legs 724A, 724B of the receiving member 708. Each wire 551 maybe tensioned to couple the percutaneous access device 650 to the boneanchor assembly 700. The wires 551 may be tensioned by, for example,retracting the wires 551 distally. Releasing the tension on the wires551 by, for example, cutting the wires 551 or advancing the wires 551proximally, can release the percutaneous access device 650 from the boneanchor assembly 700. In the illustrated exemplary embodiment, thepercutaneous access device 650 includes a single tube, outer tube 652;an inner tube may be provided but is not necessary.

FIG. 21 illustrates an alternative embodiment of a bone anchor assembly800 having one or more removable tabs 801 for releasable engagement withan instrument such as an embodiment of a percutaneous access devicedescribed above. In the illustrated exemplary embodiment, a pair ofopposing tabs 801A, 801B extend proximally from the proximal end of thereceiving member 808 of the bone anchor assembly 800. Each tab 801A,801B, in the illustrated exemplary embodiment, is generally arcuate inshape and are positioned proximal to and extend from a respective leg824A, 824B of the receiving member 808. The size, shape, and number oftabs 801 may be varied without departing from the scope of the presentinvention. The tabs 801 may include a mechanism for facilitatingreleasable engagement by an instrument. For example, the tabs may beprovided with external threads, as in the case of the embodimentillustrated in FIGS. 17A, 17B described above, or may include one ormore grooves. In the illustrated exemplary embodiment, each tab 801A,801B includes one or more arcuate grooves 830A, 830B that may beanalogous in construction to the grooves 130A, 130B described above. Thetabs 801 may include internal threads 815 to facilitate advancement of aclosure mechanism to the bone anchor assembly. Tabs 801 may be shearedoff the bone anchor assembly 800 by the percutaneous access device orinstrument or, alternatively, may be removed from the bone anchorassembly 800 after withdrawal of the percutaneous access device orinstrument using a suitable instrument.

FIGS. 22A-22B illustrates an exemplary embodiment of a percutaneousaccess device 850 having one or more axially extending cut-outs 853provided in the outer tube 852 of the percutaneous access device. Asillustrated in FIG. 22B, an axially extending cut-out 853 may facilitatethe use of multiple percutaneous access devices by minimizinginterference between the devices. For example, in certain spinalapplications, bone anchors placed on adjacent vertebrae may be closelyspaced and/or angled in a manner that may cause interference betweeninstruments, such as a percutaneous access device disclosed herein, usedsimultaneously with the adjacent bone anchors. By providing axialcut-outs 853, two or more percutaneous access devices 850A, 850B may beemployed on adjacent bone anchors, or closely positioned anchors, byaligning the cut-outs 853A, 853B. The length and depth of a cut-out 852may be varied depending on the application. One or more cut-outs may beprovided on any of the exemplary embodiments of the percutaneous accessdevice described herein or with other instruments used with boneanchors, e.g., drills, drivers, cannulas, approximators, and the like.In embodiments including an inner tube or additional tubes, theadditional tubes may also be provided with cut-outs 853.

FIGS. 23A-23B illustrates an alternative embodiment of a percutaneousaccess device 950 and a bone anchor assembly 900 in which the distal end956 of the inner tube 954 of the percutaneous access device 950 includesone or more flexible bone anchor engaging tabs 958 for releasableengagement with the receiving member 908 of bone anchor assembly 900. Inthe exemplary embodiment, a pair of opposing tabs 958A, 958B extenddistally from the distal end 956 of the inner tube 954. Each tab 958, inthe illustrated exemplary embodiment, is connected at a proximal end tothe inner tube 954 and has a free distal end 960. One or both of thetabs 958 can flex from a first position, in which the tab 958 isoriented approximately axially, e.g., parallel to the longitudinal axisof the inner tube 954, to a second position, in which the tab 958 isgenerally oriented at angle to the longitudinal axis of the inner tube954. In the exemplary embodiment, for example, each tab 958A, 958B mayflexed radially outward, e.g., away from each other, from a firstposition, in which the tabs 958A, 958B are approximately parallel, to asecond, flexed positioned, in which the tabs 958A, 958B are oriented atan angle to one another. The tabs 958 may be biased to the firstposition. For example, the tabs 958A, 958B may be biased to the first,parallel position, such that the tabs 958A, 958B may provide a radiallycompressive force on the receiving member 908 to releasably engage thereceiving member 908. One or more of the tabs 958 may be provided with aprojection or the like for engaging a hole, groove, etc, that may beprovided in the exterior surface of the receiving member 908. Althoughthe exemplary embodiment includes two tabs 958A, 958B, any number (oneor more) tabs 958 may be provided.

The percutaneous access device 950 may include an outer tube 952 thatmay be advanced about the tabs 958 when the tabs 958 releasably engagethe receiving member 908. For example, in the illustrated exemplaryembodiment, the outer tube 952 may be advanced distally about the tabs958A, 958B when the tabs are in the second, flexed position, to inhibitseparation of the tabs 958A, 958B and/or provide a radially compressiveforce on the tabs.

While the percutaneous access systems and bone anchor assemblies of thepresent invention have been particularly shown and described withreference to the exemplary embodiments thereof, those of ordinary skillin the art will understand that various changes may be made in the formand details herein without departing from the spirit and scope of thepresent invention. Those of ordinary skill in the art will recognize orbe able to ascertain many equivalents to the exemplary embodimentsdescribed specifically herein by using no more than routineexperimentation. Such equivalents are intended to be encompassed by thescope of the present invention and the appended claims.

1-46. (canceled)
 47. A bone anchor to anchor an elongated implant to apatient bone and threadably engage with a closure plug, the bone anchorfurther to couple with a tool comprising an attachment structure, thebone anchor comprising: an anchoring member comprising a distal portionand a proximal portion opposite the distal portion, the distal portionto attach to the patient bone in an anchoring manner; and a head coupledto the proximal portion of the anchoring member, the head to couple tothe elongated implant, the head comprising: a proximal end and a distalend opposite the proximal end, the proximal portion of the anchoringmember extending into the distal end such that the head is coupled tothe proximal portion of the anchoring member; a first arm and a secondarm spaced apart from the first arm to define a channel to receive theelongated implant to couple the head to the elongated implant, thechannel extending distally from the proximal end; a helically woundthread defined in an inner surface of the channel, the inner surfacefacing radially inward towards a longitudinal center axis of the head,the helically wound thread to threadably engage with the closure plugwhen the closure plug is received in the channel; an outer surfacefacing radially outward relative to the longitudinal center axis of thehead, the outer surface being on the first arm; and a horizontalradiused slot near the proximal end of the head and extending along atleast a portion of the outer surface in a direction perpendicular to thelongitudinal center axis of the head, the slot to receive the attachmentstructure when the bone anchor is coupled to the tool; and wherein thehorizontal radiused slot comprises a proximal boundary comprising aradially inner extent and a radially outer extent radially outward ofthe radially inner extent, wherein the radially outer extent is distalthe radially inner extent.
 48. The bone anchor of claim 47, wherein,when the bone anchor is coupled to the tool, a free end of theattachment structure is received in a proximal recess defined by theradially inner extent and the radially outer extent.
 49. The bone anchorof claim 48, wherein the free end and the radially outer extent interactto inhibit the attachment structure from radially outward displacement.50. A bone anchor to anchor an elongated implant to a patient bone andthreadably engage with a closure plug, the bone anchor further to couplewith a tool comprising an attachment structure, the bone anchorcomprising: an anchoring member comprising a distal portion and aproximal portion opposite the distal portion, the distal portion toattach to the patient bone in an anchoring manner; and a head coupled tothe proximal portion of the anchoring member, the head to couple to theelongated implant, the head comprising: a proximal end and a distal endopposite the proximal end, the proximal portion of the anchoring memberextending into the distal end such that the head is coupled to theproximal portion of the anchoring member; a first arm and a second armspaced apart from the first arm to define a channel to receive theelongated implant to couple the head to the elongated implant, thechannel extending distally from the proximal end; a helically woundthread defined in an inner surface of the channel, the inner surfacefacing radially inward towards a longitudinal center axis of the head,the helically wound thread to threadably engage with the closure plugwhen the closure plug is received in the channel; an outer surfacefacing radially outward relative to the longitudinal center axis of thehead, the outer surface being on the first arm; and a horizontalradiused slot near the proximal end of the head and extending along atleast a portion of the outer surface in a direction perpendicular to thelongitudinal center axis of the head, the slot to receive the attachmentstructure when the bone anchor is coupled to the tool; and wherein thehorizontal radiused slot comprises a proximal boundary comprising adistal projecting lip structure and, when the bone anchor is coupled tothe tool, the attachment structure engages the distal projecting lip.51. The bone anchor of claim 50, wherein the attachment structureengaging the distal projecting lip acts to inhibit the attachmentstructure from radially outward displacement.
 52. A bone anchor toanchor an elongated implant to a patient bone and threadably engage witha closure plug, the bone anchor further to couple with a tool comprisingan attachment structure, the bone anchor comprising: an anchoring membercomprising a distal portion and a proximal portion opposite the distalportion, the distal portion to attach to the patient bone in ananchoring manner; and a head coupled to the proximal portion of theanchoring member, the head to couple to the elongated implant, the headcomprising: a proximal end and a distal end opposite the proximal end,the proximal portion of the anchoring member extending into the distalend such that the head is coupled to the proximal portion of theanchoring member; a first arm and a second arm spaced apart from thefirst arm to define a channel to receive the elongated implant to couplethe head to the elongated implant, the channel extending distally fromthe proximal end; a helically wound thread defined in an inner surfaceof the channel, the inner surface facing radially inward towards alongitudinal center axis of the head, the helically wound thread tothreadably engage with the closure plug when the closure plug isreceived in the channel; an outer surface facing radially outwardrelative to the longitudinal center axis of the head, the outer surfacebeing on the first arm; and a horizontal radiused slot near the proximalend of the head and extending along at least a portion of the outersurface in a direction perpendicular to the longitudinal center axis ofthe head, the slot to receive the attachment structure when the boneanchor is coupled to the tool; wherein the slot comprises a boundarythat comprises a structural configuration that interacts with theattachment structure to inhibit radially outward displacement of theattachment structure from the slot in which the attachment structure isreceived; and wherein the structural configuration comprises a lipstructure.
 53. The bone anchor of claim 52, wherein the boundary is aproximal boundary.
 54. A bone anchor to anchor an elongated implant to apatient bone and threadably engage with a closure plug, the bone anchorfurther to couple with a tool comprising an attachment structure, thebone anchor comprising: an anchoring member comprising a distal portionand a proximal portion opposite the distal portion, the distal portionto attach to the patient bone in an anchoring manner; and a head coupledto the proximal portion of the anchoring member, the head to couple tothe elongated implant, the head comprising: a proximal end and a distalend opposite the proximal end, the proximal portion of the anchoringmember extending into the distal end such that the head is coupled tothe proximal portion of the anchoring member; a first arm and a secondarm spaced apart from the first arm to define a channel to receive theelongated implant to couple the head to the elongated implant, thechannel extending distally from the proximal end; a helically woundthread defined in an inner surface of the channel, the inner surfacefacing radially inward towards a longitudinal center axis of the head,the helically wound thread to threadably engage with the closure plugwhen the closure plug is received in the channel; an outer surfacefacing radially outward relative to the longitudinal center axis of thehead, the outer surface being on the first arm; and a horizontalradiused slot near the proximal end of the head and extending along atleast a portion of the outer surface in a direction perpendicular to thelongitudinal center axis of the head, the slot to receive the attachmentstructure when the bone anchor is coupled to the tool; wherein theproximal end comprises a surface perpendicular to the outer surface:wherein the horizontal radiused slot is closer in proximity to theproximal end than to the distal end; and wherein a proximal boundary ofthe horizontal radiused slot comprises an undercut defining a proximalprojecting recess of the horizontal radiused slot.
 55. The bone anchorof claim 54, wherein the recess of the slot is to interact with theattachment structure to prevent radially outward displacement of theattachment structure from the slot in which the attachment structure isreceived.
 56. A bone anchor to anchor an elongated implant to a patientbone and threadably engage with a closure plug, the bone anchor furtherto couple with a tool comprising an attachment structure, the boneanchor comprising: an anchoring member comprising a distal portion and aproximal portion opposite the distal portion, the distal portion toattach to the patient bone in an anchoring manner; and a head coupled tothe proximal portion of the anchoring member, the head to couple to theelongated implant, the head comprising: a proximal end and a distal endopposite the proximal end, the proximal portion of the anchoring memberextending into the distal end such that the head is coupled to theproximal portion of the anchoring member; a first arm and a second armspaced apart from the first arm to define a channel to receive theelongated implant to couple the head to the elongated implant, thechannel extending distally from the proximal end; a helically woundthread defined in an inner surface of the channel, the inner surfacefacing radially inward towards a longitudinal center axis of the head,the helically wound thread to threadably engage with the closure plugwhen the closure plug is received in the channel; an outer surfacefacing radially outward relative to the longitudinal center axis of thehead, the outer surface being on the first arm; and a horizontalradiused slot near the proximal end of the head and extending along atleast a portion of the outer surface in a direction perpendicular to thelongitudinal center axis of the head, the slot to receive the attachmentstructure when the bone anchor is coupled to the tool; and wherein thehorizontal radiused slot comprises a planar boundary perpendicular tothe longitudinal center axis of the head and perpendicularlyintersecting the outer surface.
 57. A bone anchor to anchor an elongatedimplant to a patient bone and threadably engage with a closure plug, thebone anchor further to couple with a tool comprising an attachmentstructure near a lower end of the tool, the bone anchor comprising: ananchoring member comprising a distal portion and a proximal portionopposite the distal portion, the distal portion to be attached to thepatient bone in an anchoring manner; and a head to be coupled to andlocated near the proximal portion of the anchoring member and to coupleto the elongated implant, the head comprising: a proximal region with aproximal end, and a distal region opposite the proximal end, theproximal portion of the anchoring member extending distally from thedistal region of the head; a first arm and a second arm spaced apartfrom the first arm to define a channel therebetween to receive theelongated implant to couple the head to the elongated implant, thechannel extending distally from the proximal end of the head; ahelically wound thread defined in an inner surface on opposite sides ofthe channel, the inner surface facing radially inward towards alongitudinal center axis of the head, the helically wound thread tothreadably engage with the closure plug when the closure plug isreceived in the channel; an outer surface facing radially outwardrelative to the longitudinal center axis of the head, the outer surfacebeing on at least the first arm; and a horizontal radiused slotextending along at least a portion of the outer surface in a directionperpendicular to the longitudinal center axis of the head and radiallyspaced therefrom, the slot to receive the attachment structure when thebone anchor is coupled to the tool, the slot located near the proximalend of the head, and the proximal end of the head having a top surfacethereon wherein the horizontal radiused slot comprises a recessedoverhanging configuration at a proximal boundary of the horizontalradiused slot.
 58. A bone anchor to anchor an elongated implant to apatient bone and threadably engage with a closure plug, the bone anchorfurther to couple with a tool comprising an attachment structure near alower end of the tool, the bone anchor comprising: an anchoring membercomprising a distal portion and a proximal portion opposite the distalportion, the distal portion to be attached to the patient bone in ananchoring manner; and a head to be coupled to and located near theproximal portion of the anchoring member and to couple to the elongatedimplant, the head comprising: a proximal region with a proximal end, anda distal region opposite the proximal end, the proximal portion of theanchoring member extending distally from the distal region of the head;a first arm and a second arm spaced apart from the first arm to define achannel therebetween to receive the elongated implant to couple the headto the elongated implant, the channel extending distally from theproximal end of the head; a helically wound thread defined in an innersurface on opposite sides of the channel, the inner surface facingradially inward towards a longitudinal center axis of the head, thehelically wound thread to threadably engage with the closure plug whenthe closure plug is received in the channel; an outer surface facingradially outward relative to the longitudinal center axis of the head,the outer surface being on at least the first arm; and a horizontalradiused slot extending along at least a portion of the outer surface ina direction perpendicular to the longitudinal center axis of the headand radially spaced therefrom, the slot to receive the attachmentstructure when the bone anchor is coupled to the tool, the slot locatednear the proximal end of the head, and the proximal end of the headhaving a top surface thereon wherein the horizontal radiused slotcomprises a proximal boundary comprising a radially inner extent and aradially outer extent radially outward of the radially inner extent,wherein the radially outer extent is distal the radially inner extent.59. The bone anchor of claim 58, wherein, when the bone anchor iscoupled to the tool, a free end of the attachment structure is receivedin a proximal recess defined by the radially inner extent and theradially outer extent.
 60. The bone anchor of claim 59, wherein the freeend and the radially outer extent interact to inhibit the attachmentstructure from radially outward displacement.
 61. The bone anchor ofclaim 57, wherein the bone screw is a polyaxial bone screw.